Enlighten the newbie on amps :)
Mar 17, 2006 at 9:07 AM Thread Starter Post #1 of 17

Ruahrc

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Hello-

Way back in the day I was as oblivious as the next guy, more bass is better and the cooler looking headphones are the better they must be
smily_headphones1.gif
. But then I discovered Head-fi (and my poor unfortunate wallet). I learned about good headphones and stepped up to entry-level audiofidelity and re-encoded my music library (at the time it was 96-128kbps wma ouch!) into high quality format (EAC ripped Lame encoded "alt preset standard" VBR) and got some good headphones (KSC-35 and Ety ER-4P). I had read a little about amps and that they were the next level of headphone listening but never really experienced "amped" audio or read too much about it.

Now I'm curious. I have some basic questions about headphone amps. First of all- what do they do exactly? I am confused on the concept of an amp- because it seems to me like adding additional devices in the audio chain from the source to your ears can only degrade the audio, since it can't ever really improve the audio that it recieves from the previous source. I also read that the high echelons of headphones pretty much require an amp to be used to their potential- and if you buy an expensive set of headphones and use them without an amp you are basically neglecting 75% of their performance capability.

For example- if I go straight from my 2G iPod (my only real "source" BTW- like I said I'm at entry-level audiophile still) into a pair of headphones, versus iPod>amp>cans- does that not introduce an extra device which can degrade signal quality, or extra connections to reduce signal quality, etc?

I know enough (or do I...) to know that amps are not really used for their volume-enhancing properties... but how does that all work? I guess ideally you are using line-level sources (which actually are extremely loud, if you plugged headphones straight into a line-out port right?) and the amp actually attenuates the volume and makes it adjustable via variable levels of gain.

Would not the "ideal" amp be merely a volume attenuator from the line-level source? (I guess that's why you can buy a $1000 pot!?) Why would you introduce extra elements into the audio path if you can take the unadulterated line-level audio coming straight from the source and reduce it to a listenable level?

Unless it is the "flavor" or "interpretation" of the music that the amp imparts onto the audio which people are after? A rough analogy of what I'm trying to say might be having different orchestras play the same piece of music. Each will play it slightly different, and some people might prefer this orchestra or that- based on the type of music they listen to. Obviously listening to a particular song played by the London Philharmonic vs. Podunk's High School Orchestra will provide pretty clear indications of "better" and "worse", but there are also many "lateral" comparisons where better and worse aren't as appropriate as "different". So the London Philharmonic might be the $5000 amp + $3000 headphones and the high school orchestra be the el cheapo amp one might find in a standard consumer-grade electronic (like PCDP or iPod)?

So- I'm looking for kind of an "introduction to amps"... even links to webpages where this has been previously hashed out would be great. I'm just curious to see what it's all about. Although I do not plan on entering the "amp arena" in the near future I could forsee myself eventually buying an amp to enhance my ER-4P's (when using the 4P>4S converter cable?) or any other headphone I pick up in the future.

Anyways, thanks for reading and I would love to hear some replies to help me understand
smily_headphones1.gif


Ruahrc
 
Mar 17, 2006 at 5:38 PM Post #2 of 17

jcx

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http://headwize.com/library.htm

look through the articles and technical papers

look for a basic explaination of electircal power:

Watts =Amps * Volts

and

Volts = Amps * Resistance

some algebra lets you understand Hi Z (Z = impedance ~= Resistance) vs Lo Z headphones and amplifier current and voltage relations

(and rms vs peak values)

then some understanding of dB (Decibel power ratio) and SPL (Sound Pressure Level) is needed to become conversant in amplifier/headphone concepts
 
Mar 17, 2006 at 8:45 PM Post #3 of 17

c0mfortably_numb

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Quote:

Originally Posted by Ruahrc
Hello-
For example- if I go straight from my 2G iPod (my only real "source" BTW- like I said I'm at entry-level audiophile still) into a pair of headphones, versus iPod>amp>cans- does that not introduce an extra device which can degrade signal quality, or extra connections to reduce signal quality, etc?
Ruahrc



Good question, basically what you are doing is amplifying the signal coming out of the headphone jack. Most portable devices provide in the neighborhood of 2-15 millawatts...a dedicated headphone amp provides upwards of 300mw or more. 2-15mw is fine if you do not know any better and use cans from your local Mega Rip Off Mart....

Now if you want a clean source for your new amp (to which I wanted) then you can purchase a dock that will provide a 'LINE OUT' which totally bypasses the internal headphone amplifier...Such devices are SIK Din and there are a few others..I never tried any but the home made one by Head-Fier Turbo, and its called TurbodockII...I much prefer the sound of my Ipod useing the dock to line out. The sound is just so much more brilliant IMHO, there is no other circuits getting in the way of the dedicated headphone amp. Also to note do not hook headphones up directly to a line out can spell bad news to your source, your cans or both....neither were built to handle the load...so if going line out make sure to have a dedicated headphone amp
smily_headphones1.gif


Now as far as Headphone amps go, its all in the matter of what are you looking for in sound? Me personally I wanted tighter and faster bass response and overally just a better sound from my Grados. I found that by purchasing a buffered op amp <custom built Pimeta>

So first things first take stock of what you have, IE: are you going to stick with the Ipod as a source or upgrade? Are you going to stick with those cans? What kind of music do you listen to?
 
Mar 17, 2006 at 9:43 PM Post #4 of 17

Jaguar

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Hey Comfortably Numb,
I'm not the original poster, but thanks for the nice summary of what heaphone amps do. Next on my list is a Turbodock.

-Jag
cool.gif
 
Mar 17, 2006 at 10:19 PM Post #5 of 17

c0mfortably_numb

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Quote:

Originally Posted by Jaguar
Hey Comfortably Numb,
I'm not the original poster, but thanks for the nice summary of what heaphone amps do. Next on my list is a Turbodock.

-Jag
cool.gif



Glade to be of some assistance
smily_headphones1.gif
When you get the dock post your impression...so far everyone I let listen to at work at first thought I was crazy or on drugs for spending as much as I have...then they hear my portable rig and there like how do I go about putting something like this together, were do I get all the parts..LOL
 
Mar 17, 2006 at 11:07 PM Post #6 of 17

Bones13

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I bet you can find a $1000 pot
580smile.gif


Advice - listen and be amazed
 
Mar 22, 2006 at 3:03 AM Post #7 of 17

Ruahrc

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Quote:

Originally Posted by c0mfortably_numb
Good question, basically what you are doing is amplifying the signal coming out of the headphone jack. Most portable devices provide in the neighborhood of 2-15 millawatts...a dedicated headphone amp provides upwards of 300mw or more. 2-15mw is fine if you do not know any better and use cans from your local Mega Rip Off Mart....


But here's the part I'm missing: if 15mw is sufficient to drive rip-off-cans to extremely high volume levels (for example stock iPod and iPod buds can go near or over 100dB) then what would happen when you connect it to a 300mw amp? They'd be like loudspeakers?

Clearly there is not a straightforward relationship between power output and volume level output, right? If I plugged say a Sennheiser HD650 into an iPod (no amp), you're saying I would barely hear anything, even with the volume up to the max... since they require more power to run?

I'm guessing there's also a quantity vs. quality factor here too- for much as in the world of speakers, 400W output don't mean jack unless it's 400 QUALITY watts. Meaning it'll be "400W loud" but also sound good at high volumes.

I understand electrical concepts so it is okay to get a little technical... what I don't really understand is how those electrical concepts translate into sound quality. For example- would it be fair to say that most high-end headphones are high-impedance headphones? That means that they will require more power (hence an amp) to be used properly. But is it the fact that they have high impedance the reason they sound good, or is high impedance a by-product (or penalty, if you will) of having a good sound?

There exists headphones which sound good without amps. For example, ER-4P, KSC35, even high end stuff like HD650s. Granted I would expect you would argue that all of the above 3 headphones sound better when amped, yes? But if the amp is there merely for more power (and as my current understanding: more power = more volume)... then the amps do nothing save make said headphones louder, right? So where is the benefit in quality coming from?

Ruahrc
 
Mar 22, 2006 at 3:17 AM Post #8 of 17

003

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Quote:

Originally Posted by Ruahrc
For example- would it be fair to say that most high-end headphones are high-impedance headphones?


No, not really. All headphones benefit from amping (or so I hear), some just more than others (the high impedance ones).
 
Mar 22, 2006 at 3:26 AM Post #9 of 17

lekun

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Yeah, this has always been a sticking point for me too, when it comes to AMPs.

For example, I don't want my Grados to get any louder, but I assume a headphone amp will somehow make the music sound better even at lower volume levels, though I can't explain why. This is why I don't own a headphone amp.
 
Mar 22, 2006 at 4:22 AM Post #10 of 17

c0mfortably_numb

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It's all about effenciency....sure a an Ipod at 2 or 3mw will play the music through the cans. Will it sound as good as if there was a cleaner source IE a dedicated headphone amp. Depending on the cans...lets take the Grado's for instance they are easy to drive and can be hooked to dang near anything with a 3.5mm jack it will sound good maybe kinda bright...lacking in bass...Now hook up a dedicated amp lets take one of the more popular options here the PocketAmp2 V2 your going to hook up a mini to mini interconnect cable to your headphone jack and set the volume on the source to about 65% and use the amp to adjust the sound. The sound will have more detailed bass response and over all just a better sound quality to it. (You can also hook up to a line out say on a portable disc player or get a dock to line out converter for the ipod)

Il try to give a better example...Car audio sure you can get a componet speaker set and hook it up to the stereo in your car...It will play right? But how good will it sound...not great...but it sounds ok. Now hook up a dedicated amp to the serperates and they just come alive.

So what Im trying to get to, is the cleaner the source, the better the sound.
580smile.gif
 
Mar 22, 2006 at 6:30 AM Post #11 of 17

fewtch

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Quote:

Originally Posted by lekun
Yeah, this has always been a sticking point for me too, when it comes to AMPs.

For example, I don't want my Grados to get any louder, but I assume a headphone amp will somehow make the music sound better even at lower volume levels, though I can't explain why. This is why I don't own a headphone amp.



Grados are low impedance, and thus current-hungry. If you got a buffered amp, it's likely to clear up some distortions you didn't even know were there using it from a stock headphone jack. Also, if you get a standalone source that has line level RCA outputs, you're going to want an amp for that.
 
Mar 22, 2006 at 8:07 AM Post #12 of 17

Ruahrc

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Quote:

Originally Posted by c0mfortably_numb
It's all about effenciency....sure a an Ipod at 2 or 3mw will play the music through the cans. Will it sound as good as if there was a cleaner source IE a dedicated headphone amp. Depending on the cans...lets take the Grado's for instance they are easy to drive and can be hooked to dang near anything with a 3.5mm jack it will sound good maybe kinda bright...lacking in bass...Now hook up a dedicated amp lets take one of the more popular options here the PocketAmp2 V2 your going to hook up a mini to mini interconnect cable to your headphone jack and set the volume on the source to about 65% and use the amp to adjust the sound. The sound will have more detailed bass response and over all just a better sound quality to it. (You can also hook up to a line out say on a portable disc player or get a dock to line out converter for the ipod)


I can understand cleaner source=cleaner sound (and btw I don't consider an amp a source persay. It does not originate audio signals, it requires an input signal to produce an output) but in your example (PocketAmp2 V2) I don't see how the source gets cleaner by adding another device in the signal path. Distorted signal coming out of the source (through the source's headphone amp?) and into the PocketAmp and somehow the PocketAmp is able to clean the noise out of the signal and restore it to its pristine state? Not from what I understand... distorted signal is like smudging a painting. You can't "smudge it back" or fix it.. once you smudge out that detail it is lost unless you actually go back and re-paint it. And I really don't believe that amps are re-creating audio signal on-the-fly
smily_headphones1.gif


Perhaps I can see the merit of bypassing a built-in headphone amp in say an iPod and going line out>good amp- but again if the goal is to preserve original signal quality as best as possible- wouldn't it be even better to just have no amp at all? Just attenuate the signal coming off of the line-out source and get it into your headphones... nothing to mess up the signal in between. Maybe I don't understand line-out signal electronics like I should...

Or maybe you are trying to tell me that amps are like headphones in a way? Each headphone has a unique characteristic, and one must choose a headphone based on his/her music preferences as well as aural preferences. As such each amp sounds a little different (again... there is a point in which amps stop sounding "better" and merely become "different"?) and one must pick an amp that fits their listening style. The amp, strictly speaking, distorts or alters the signal coming off the source but in this case it is a positive thing because it changes the sound to the preference of the listener. There are also others out there who prefer absolute signal fidelity- and as such I have read in threads here of people driving headphones direct off line-outs in order to mimize signal alteration between the audio source and the headphone driver.

PS I hope I do not come across as argumentative. I am only trying to understand and learn about the purpose of amps- and the best way to understand is to keep asking the questions
smily_headphones1.gif


Ruahrc
 
Mar 22, 2006 at 6:29 PM Post #13 of 17

jcx

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2 big concepts needed:

I.How Loud? – Sound Pressure level

http://headwize.com/articles/hearing_art.htm

Read twice – Once to avoid hearing loss, a second reading to determine the dynamic range of live music and the peak SPL required (for only minutes or seconds ) to cleanly reproduce real music



II.Electrical Power/Impedance relations and Headphone Sensitivity

All amplifiers have a limited range of Voltage and Current which they can supply

Unlike loudspeakers, headphone Impedances are not standardized and (commonly available) different models range ~ 40:1 (16 Ohm iPod canal phones to 600 Ohm DT990 pro monitoring phones)

Voltage and Current is required to provide the power (in milliwatts, 1 mW is the ref level for headphone sensitivity) to different headphones – basic electricity: power in a Resistor relations are needed - different ratios of peak Voltage to Peak current are required to drive different Impedance headphones with the same power, different Sensitivity headphones need different Power for the same SPL

Example:

IPod ~ 1 Vrms output into 16 Ohm canal phones gives ~ 60 mWrms power

The amplifier chip for maxim in the iPod is designed for low voltage, high current output ~80 mA peak current is required for 60 mWrms into 16 Ohms

Sensitivity for the iPod: 105 dB SPL / mW input power (typical of canal phones)

10 * Log( 60 mW / 1 mW) = + 17.8 dB power (re 1mW)

max SPL = 105 + 17.8 ~= 123 dB SPL – loud enough to hurt but surprisingly not always enough to reproduce live music levels:

symphonic music peak 120 - 137 dB


Now plug the Senn HD600 at 300 Ohms and 97 dB/mW into a iPod:

(1 Vrms)^2 / 300 Ohm ~= 3 mW => ~ +5 dBm

5 dB power + 97 dB sensitivity = 102 dB max SPL

- I think you will want an external amp, one that puts out more Voltage than the iPod

To get the same 123 dB SPL out of the HD600: 123 - 97 = 26 dB power re 1 mW

26 dB => 10^(26/10) = 400 mWrms

( 400 mW * 300 Ohms )^(1/2) = 11 Vrms

=> ~ 15 Vpeak, 50 mA peak

The iPod simply can't swing that much Voltage from its 3.6 V Li battery


Headphone Sensitivity and Impedance

http://headwize.com/tech/dbohn1_tech.htm

which contains the page:

http://headwize.com/tech/dbohn1_table.htm


To see what amps match up with which headphone you need to know the amp’s Voltage swing and undistorted Current output limits and the headphone Impedance and Sensitivity
 
Apr 3, 2006 at 5:00 AM Post #14 of 17

Jaguar

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Quote:

Originally Posted by c0mfortably_numb
Glade to be of some assistance
smily_headphones1.gif
When you get the dock post your impression...so far everyone I let listen to at work at first thought I was crazy or on drugs for spending as much as I have...then they hear my portable rig and there like how do I go about putting something like this together, were do I get all the parts..LOL



Got my Turbodock yesterday and I'm very happy with it. This is my current setup...

4G 40gb iPod > Turbodock II > PA2V2 > Senn HD 595

The sound quality has noticeably improved compared to using the headphone jack. Thanks for recommendation.

-Jag
cool.gif
 
Apr 3, 2006 at 7:57 PM Post #15 of 17

TheBoxesPlace

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The need for an amp was explained to me in very simple terms as follows:
We have all taken an IPOD, car stereo, hand held radio, etc and turned the volume all the way up. What you get is loud sound levels but also a lot of distortion. Thats because the sources amp was using close to 100% of its capacity.
Now add a more powerful separate amp, bypass the headphone jack by using the line out and now what do you get?
You get the same loudness without having to turn the amp all the way up. So for example you may only be using 10% of the amps capacity to achieve the same sound level, BUT without the distortion.
In other words, a dedicated amp has more power so it is not pushed has hard as an IPOD headphone out amp. It doesn't clean up the sound, but more importantly it will not introduce as much distortion for a given volume level.
Doesn't a 300 Horsepower car get to 65 MPH with much less effort and strain than a 160 Horsepower car? Kinda the same idea. Its all about having reserve capacity.
 

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